linux/drivers/w1/masters/w1-uart.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * w1-uart - UART 1-Wire bus driver
 *
 * Uses the UART interface (via Serial Device Bus) to create the 1-Wire
 * timing patterns. Implements the following 1-Wire master interface:
 *
 * - reset_bus: requests baud-rate 9600
 *
 * - touch_bit: requests baud-rate 115200
 *
 * Author: Christoph Winklhofer <cj.winklhofer@gmail.com>
 */

#include <linux/completion.h>
#include <linux/delay.h>
#include <linux/jiffies.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/of.h>
#include <linux/serdev.h>
#include <linux/w1.h>

/* UART packet contains start and stop bit */
#define W1_UART_BITS_PER_PACKET (BITS_PER_BYTE + 2)

/* Timeout to wait for completion of serdev-receive */
#define W1_UART_TIMEOUT msecs_to_jiffies(500)

/**
 * struct w1_uart_config - configuration for 1-Wire operation
 * @baudrate: baud-rate returned from serdev
 * @delay_us: delay to complete a 1-Wire cycle (in us)
 * @tx_byte: byte to generate 1-Wire timing pattern
 */
struct w1_uart_config {
	unsigned int baudrate;
	unsigned int delay_us;
	u8 tx_byte;
};

/**
 * struct w1_uart_device - 1-Wire UART device structure
 * @serdev: serial device
 * @bus: w1-bus master
 * @cfg_reset: config for 1-Wire reset
 * @cfg_touch_0: config for 1-Wire write-0 cycle
 * @cfg_touch_1: config for 1-Wire write-1 and read cycle
 * @rx_byte_received: completion for serdev receive
 * @rx_mutex: mutex to protect rx_err and rx_byte
 * @rx_err: indicates an error in serdev-receive
 * @rx_byte: result byte from serdev-receive
 */
struct w1_uart_device {
	struct serdev_device *serdev;
	struct w1_bus_master bus;

	struct w1_uart_config cfg_reset;
	struct w1_uart_config cfg_touch_0;
	struct w1_uart_config cfg_touch_1;

	struct completion rx_byte_received;
	/*
	 * protect rx_err and rx_byte from concurrent access in
	 * w1-callbacks and serdev-receive.
	 */
	struct mutex rx_mutex;
	int rx_err;
	u8 rx_byte;
};

/**
 * struct w1_uart_limits - limits for 1-Wire operations
 * @baudrate: Requested baud-rate to create 1-Wire timing pattern
 * @bit_min_us: minimum time for a bit (in us)
 * @bit_max_us: maximum time for a bit (in us)
 * @sample_us: timespan to sample 1-Wire response
 * @cycle_us: duration of the 1-Wire cycle
 */
struct w1_uart_limits {
	unsigned int baudrate;
	unsigned int bit_min_us;
	unsigned int bit_max_us;
	unsigned int sample_us;
	unsigned int cycle_us;
};

static inline unsigned int baud_to_bit_ns(unsigned int baud)
{
	return NSEC_PER_SEC / baud;
}

static inline unsigned int to_ns(unsigned int us)
{
	return us * NSEC_PER_USEC;
}

/*
 * Set baud-rate, delay and tx-byte to create a 1-Wire pulse and adapt
 * the tx-byte according to the actual baud-rate.
 *
 * Reject when:
 * - time for a bit outside min/max range
 * - a 1-Wire response is not detectable for sent byte
 */
static int w1_uart_set_config(struct serdev_device *serdev,
			      const struct w1_uart_limits *limits,
			      struct w1_uart_config *w1cfg)
{
	unsigned int packet_ns;
	unsigned int bits_low;
	unsigned int bit_ns;
	unsigned int low_ns;

	w1cfg->baudrate = serdev_device_set_baudrate(serdev, limits->baudrate);
	if (w1cfg->baudrate == 0)
		return -EINVAL;

	/* Compute in nanoseconds for accuracy */
	bit_ns = baud_to_bit_ns(w1cfg->baudrate);
	bits_low = to_ns(limits->bit_min_us) / bit_ns;
	/* start bit is always low */
	low_ns = bit_ns * (bits_low + 1);

	if (low_ns < to_ns(limits->bit_min_us))
		return -EINVAL;

	if (low_ns > to_ns(limits->bit_max_us))
		return -EINVAL;

	/* 1-Wire response detectable for sent byte */
	if (limits->sample_us > 0 &&
	    bit_ns * BITS_PER_BYTE < low_ns + to_ns(limits->sample_us))
		return -EINVAL;

	/* delay: 1-Wire cycle takes longer than the UART packet */
	packet_ns = bit_ns * W1_UART_BITS_PER_PACKET;
	w1cfg->delay_us = 0;
	if (to_ns(limits->cycle_us) > packet_ns)
		w1cfg->delay_us =
			(to_ns(limits->cycle_us) - packet_ns) / NSEC_PER_USEC;

	/* byte to create 1-Wire pulse */
	w1cfg->tx_byte = 0xff << bits_low;

	return 0;
}

/*
 * Configuration for reset and presence detect
 * - bit_min_us is 480us, add margin and use 485us
 * - limits for sample time 60us-75us, use 65us
 */
static int w1_uart_set_config_reset(struct w1_uart_device *w1dev)
{
	struct serdev_device *serdev = w1dev->serdev;
	struct device_node *np = serdev->dev.of_node;

	struct w1_uart_limits limits = { .baudrate = 9600,
					 .bit_min_us = 485,
					 .bit_max_us = 640,
					 .sample_us = 65,
					 .cycle_us = 960 };

	of_property_read_u32(np, "reset-bps", &limits.baudrate);

	return w1_uart_set_config(serdev, &limits, &w1dev->cfg_reset);
}

/*
 * Configuration for write-0 cycle (touch bit 0)
 * - bit_min_us is 60us, add margin and use 65us
 * - no sampling required, sample_us = 0
 */
static int w1_uart_set_config_touch_0(struct w1_uart_device *w1dev)
{
	struct serdev_device *serdev = w1dev->serdev;
	struct device_node *np = serdev->dev.of_node;

	struct w1_uart_limits limits = { .baudrate = 115200,
					 .bit_min_us = 65,
					 .bit_max_us = 120,
					 .sample_us = 0,
					 .cycle_us = 70 };

	of_property_read_u32(np, "write-0-bps", &limits.baudrate);

	return w1_uart_set_config(serdev, &limits, &w1dev->cfg_touch_0);
}

/*
 * Configuration for write-1 and read cycle (touch bit 1)
 * - bit_min_us is 5us, add margin and use 6us
 * - limits for sample time 5us-15us, use 15us
 */
static int w1_uart_set_config_touch_1(struct w1_uart_device *w1dev)
{
	struct serdev_device *serdev = w1dev->serdev;
	struct device_node *np = serdev->dev.of_node;

	struct w1_uart_limits limits = { .baudrate = 115200,
					 .bit_min_us = 6,
					 .bit_max_us = 15,
					 .sample_us = 15,
					 .cycle_us = 70 };

	of_property_read_u32(np, "write-1-bps", &limits.baudrate);

	return w1_uart_set_config(serdev, &limits, &w1dev->cfg_touch_1);
}

/*
 * Configure and open the serial device
 */
static int w1_uart_serdev_open(struct w1_uart_device *w1dev)
{
	struct serdev_device *serdev = w1dev->serdev;
	struct device *dev = &serdev->dev;
	int ret;

	ret = devm_serdev_device_open(dev, serdev);
	if (ret < 0)
		return ret;

	ret = serdev_device_set_parity(serdev, SERDEV_PARITY_NONE);
	if (ret < 0) {
		dev_err(dev, "set parity failed\n");
		return ret;
	}

	ret = w1_uart_set_config_reset(w1dev);
	if (ret < 0) {
		dev_err(dev, "config for reset failed\n");
		return ret;
	}

	ret = w1_uart_set_config_touch_0(w1dev);
	if (ret < 0) {
		dev_err(dev, "config for touch-0 failed\n");
		return ret;
	}

	ret = w1_uart_set_config_touch_1(w1dev);
	if (ret < 0) {
		dev_err(dev, "config for touch-1 failed\n");
		return ret;
	}

	serdev_device_set_flow_control(serdev, false);

	return 0;
}

/*
 * Send one byte (tx_byte) and read one byte (rx_byte) via serdev.
 */
static int w1_uart_serdev_tx_rx(struct w1_uart_device *w1dev,
				const struct w1_uart_config *w1cfg, u8 *rx_byte)
{
	struct serdev_device *serdev = w1dev->serdev;
	int ret;

	serdev_device_write_flush(serdev);
	serdev_device_set_baudrate(serdev, w1cfg->baudrate);

	/* write and immediately read one byte */
	reinit_completion(&w1dev->rx_byte_received);
	ret = serdev_device_write_buf(serdev, &w1cfg->tx_byte, 1);
	if (ret != 1)
		return -EIO;
	ret = wait_for_completion_interruptible_timeout(
		&w1dev->rx_byte_received, W1_UART_TIMEOUT);
	if (ret <= 0)
		return -EIO;

	/* locking could fail when serdev is unexpectedly receiving. */
	if (!mutex_trylock(&w1dev->rx_mutex))
		return -EIO;

	ret = w1dev->rx_err;
	if (ret == 0)
		*rx_byte = w1dev->rx_byte;

	mutex_unlock(&w1dev->rx_mutex);

	if (w1cfg->delay_us > 0)
		fsleep(w1cfg->delay_us);

	return ret;
}

static size_t w1_uart_serdev_receive_buf(struct serdev_device *serdev,
					  const u8 *buf, size_t count)
{
	struct w1_uart_device *w1dev = serdev_device_get_drvdata(serdev);

	mutex_lock(&w1dev->rx_mutex);

	/* sent a single byte and receive one single byte */
	if (count == 1) {
		w1dev->rx_byte = buf[0];
		w1dev->rx_err = 0;
	} else {
		w1dev->rx_err = -EIO;
	}

	mutex_unlock(&w1dev->rx_mutex);
	complete(&w1dev->rx_byte_received);

	return count;
}

static const struct serdev_device_ops w1_uart_serdev_ops = {
	.receive_buf = w1_uart_serdev_receive_buf,
	.write_wakeup = serdev_device_write_wakeup,
};

/*
 * 1-wire reset and presence detect: A present slave will manipulate
 * the received byte by pulling the 1-Wire low.
 */
static u8 w1_uart_reset_bus(void *data)
{
	struct w1_uart_device *w1dev = data;
	const struct w1_uart_config *w1cfg = &w1dev->cfg_reset;
	int ret;
	u8 val;

	ret = w1_uart_serdev_tx_rx(w1dev, w1cfg, &val);
	if (ret < 0)
		return -1;

	/* Device present (0) or no device (1) */
	return val != w1cfg->tx_byte ? 0 : 1;
}

/*
 * 1-Wire read and write cycle: Only the read-0 manipulates the
 * received byte, all others left the line untouched.
 */
static u8 w1_uart_touch_bit(void *data, u8 bit)
{
	struct w1_uart_device *w1dev = data;
	const struct w1_uart_config *w1cfg = bit ? &w1dev->cfg_touch_1 :
						   &w1dev->cfg_touch_0;
	int ret;
	u8 val;

	ret = w1_uart_serdev_tx_rx(w1dev, w1cfg, &val);

	/* return inactive bus state on error */
	if (ret < 0)
		return 1;

	return val == w1cfg->tx_byte ? 1 : 0;
}

static int w1_uart_probe(struct serdev_device *serdev)
{
	struct device *dev = &serdev->dev;
	struct w1_uart_device *w1dev;
	int ret;

	w1dev = devm_kzalloc(dev, sizeof(*w1dev), GFP_KERNEL);
	if (!w1dev)
		return -ENOMEM;
	w1dev->bus.data = w1dev;
	w1dev->bus.reset_bus = w1_uart_reset_bus;
	w1dev->bus.touch_bit = w1_uart_touch_bit;
	w1dev->serdev = serdev;

	init_completion(&w1dev->rx_byte_received);
	mutex_init(&w1dev->rx_mutex);

	ret = w1_uart_serdev_open(w1dev);
	if (ret < 0)
		return ret;
	serdev_device_set_drvdata(serdev, w1dev);
	serdev_device_set_client_ops(serdev, &w1_uart_serdev_ops);

	return w1_add_master_device(&w1dev->bus);
}

static void w1_uart_remove(struct serdev_device *serdev)
{
	struct w1_uart_device *w1dev = serdev_device_get_drvdata(serdev);

	/*
	 * Waits until w1-uart callbacks are finished, serdev is closed
	 * and its device data released automatically by devres (waits
	 * until serdev-receive is finished).
	 */
	w1_remove_master_device(&w1dev->bus);
}

static const struct of_device_id w1_uart_of_match[] = {
	{ .compatible = "w1-uart" },
	{},
};
MODULE_DEVICE_TABLE(of, w1_uart_of_match);

static struct serdev_device_driver w1_uart_driver = {
	.driver	= {
		.name		= "w1-uart",
		.of_match_table = w1_uart_of_match,
	},
	.probe	= w1_uart_probe,
	.remove	= w1_uart_remove,
};

module_serdev_device_driver(w1_uart_driver);

MODULE_DESCRIPTION("UART w1 bus driver");
MODULE_AUTHOR("Christoph Winklhofer <cj.winklhofer@gmail.com>");
MODULE_LICENSE("GPL");